Die-casting mold and method for thin-walled electrical connector shells

ABSTRACT

The present invention discloses a die-casting mold structure for a thin-walled shell for electrical connectors and a method for designing the mold structure. The runner of the mold structure includes a longitudinal runner, a transverse runner, an end runner, and an in-gate connected sequentially. The cross-sectional areas of the longitudinal runner, the transverse runner, the end runner, and the in-gate decrease progressively. The cross sections of the longitudinal runner and the transverse runner may be oval or circular in shape. The perimeter-to-area ratio of the oval cross section of the longitudinal runner and of the transverse runner is smaller than the ratio for a runner with a rectangular cross section of the same area. The method may be used to calculate the in-gate area. Cold shuts and gas entrapment during the molding process are reduced, enhancing the quality of the thin-walled shell and raising the efficiency of the design process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority, under the Paris Convention, of Chinese patent application, application number 201310292972.8, filed on Jul. 12, 2013 in the Intellectual Property Office of the People's Republic of China. The disclosure of the Chinese application is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to technology for manufacturing electrical connectors and, in particular, to a die-casting mold for manufacturing thin-walled shells for electrical connectors and a method for designing the die-casting mold. 2. Description of Related Art

An important component of an electrical connector, such as an HDMI interface (High-Definition Multimedia Interface) connector or other digital audio/video interface, is a thin-walled shell. Traditionally, thin-walled shells for electrical connectors are manufactured by sheet metal stamping, but in some cases, die-casting is used. For example, thin-walled connector shells that have a thickness of more than 1 mm may be manufactured using a conventional die-casting mold structure. The conventional die-casting mold structure has a runner structure that includes longitudinal runners, transverse runners, end runners, and in-gates. In the conventional die-casting mold structure, the in-gates have a rectangular cross-section, and all the runners may also have rectangular cross sections. Increasingly, thin-walled connector shells are constructed of alloy castings thinner than 1 mm. To manufacture the thin-walled shells, the size of cross-sectional areas of the runners should be reduced. Reduction in the size of cross-sectional areas is conventionally achieved by proportionally reducing the die-casting mold structure used to manufacture connector shells thicker than 1 mm. However, merely reducing the conventional die-casting mold structure to manufacture thin-walled connector shells may lead to manufacturing problems. These problems, which may include cold shuts and gas entrapment, reduce the product yield of the thin-walled connector shells and increase the cost of manufacturing.

As such, it is desirable to provide an improved die-casting mold structure for manufacturing thin-walled connector shells that solves the shortcomings of the conventional structure, preventing or reducing the occurrence of cold shuts and gas entrapment, and thereby increasing the product yield and reducing the cost of manufacturing.

SUMMARY OF THE INVENTION

A first objective of the present invention is to provide a die-casting mold structure for a thin-walled shell for electrical connectors which may overcome the shortcomings of the conventional die-casting mold structure. The die-casting mold structure may prevent or reduce the occurrence of cold shuts and gas entrapment during the molding process, thus possibly increasing the product yield of the thin-walled connector shells and reducing manufacturing costs.

A second objective of the present invention is to provide a method for designing a die-casting mold structure for a thin-walled shell for electrical connectors which can overcome the shortcomings of the conventional die-casting process.

To achieve the first objective, a die-casting mold structure for a thin-walled shell for electrical connectors is disclosed. The die-casting mold structure may include a runner structure, a mold cavity, and an overflow. The runner structure may include a longitudinal runner, a transverse runner, an end runner, and an in-gate that are connected sequentially. The cross-sectional areas of the longitudinal runner, the transverse runner, the end runner, and the in-gate may decrease progressively in the direction of flow of the molten metal. The cross section of the longitudinal runner may be oval or circular in shape. Similarly, the cross section of the transverse runner may be oval or circular in shape. The ratio of the perimeter to the area of the oval or circular cross section of the longitudinal runner or the transverse runner is smaller than the ratio for a runner with a rectangular or square cross section of the same area.

In the die-casting mold structure, the longitudinal runner and the transverse runner may be connected by a first curved runner; the transverse runner and the end runner may be connected by a second curved runner; and the end runner and the in-gate may be connected by a third curved runner.

In one embodiment, each of the first, second, and third curved runners may be an arc-shaped structure. The first curved runner may have a radius of curvature (R1) greater than 0.45*L1 and less than 0.7*L1 (0.45 L1<R1<0.7L1); the second curved runner may have a radius of curvature (R2) greater than 0.4*L2 and less than 0.6*L2 (0.4 L2<R2<0.6 L2); and the third curved runner may have a radius of curvature (R3) greater than 0.3*L2 and less than 0.5*L2 (0.3 L2<R3<0.5 L2), where L1 is the length of the transverse runner, and L2 is the length of the end runner.

In one embodiment, the longitudinal runner may be split into two transverse runners. In another embodiment, the transverse runner may be split into two end runners. In another embodiment, the height (H) of the in-gate is between 0.2*A and 0.5*A, and the width (W) of the in-gate is A/H, where A is the area of the in-gate.

To achieve the second objective, a method for designing a die-casting mold structure for a thin-walled shell for electrical connectors is disclosed. The method may calculate the area of an in-gate. The method includes:

-   -   (1) Determining an alloy that is applicable to the thin-walled         shell for an electrical connector and setting the density(ρ) of         the alloy to be 6.8 g/cm3;     -   (2) calculating the sum (G) of the mass of the thin-walled shell         for the electrical connector in the mold cavity and the mass of         the metal from the overflow: G=X+Y, where X: Y=2:1, X is the         mass of the thin-walled shell for the electrical connector in         the mold cavity, and Y is the mass of the metal from the         overflow; and     -   (3) calculating the area (A) of the in-gate:         A=0.8948+0.4292*G−0.01040*G².

The advantages of the present invention are summarized below. The shape of the cross section of the longitudinal runner is oval or circular. Similarly, the shape of the cross section of the transverse runner is oval or circular. The ratio of the perimeter (also called wet perimeter) to the area of the oval or circular cross section of the longitudinal runner or the transverse runner is smaller than the ratio for a runner with a rectangular or square cross section of the same area. As a result, the resistive and thermal loss due to the viscosity of the molten or liquid metal may be reduced. In other words, the surface resistance and the heat loss of the liquid metal may be reduced, so that the mold cavity for die-casting the thin-walled shell may keep the metal at a high-temperature molten state, thereby alleviating the problem of cold shuts. Furthermore, since the oval or circular cross section of the longitudinal and transverse runners produces walls that are smooth and without any sharp angles, when the walls are subjected to the high speed of the molten or liquid metal of the die-casting process, it is harder for gases to become entrapped in the molten metal because the possibility of local vortexes occurring in the molten metal is reduced.

Furthermore, in the filling process, the in-gate area has a significant effect on the molding quality of the thin-walled shell for electrical connectors. A quadratic function may be used to describe the relationship between the total mass (G), which is the sum of the mass of the thin-walled shell for the electrical connector in the mold cavity and the mass of the metal from the overflow, and the area (A) of the in-gate. Using the quadratic function, the area of the in-gate may be obtained quickly according to the requirement of the casting, such as a requirement for the total mass of the casting. Therefore, the time required for designing the die-casting mold structure for a thin-walled shell of an electrical connector may be reduced significantly, thereby enhancing the efficiency of the design process. In addition, the quality of the casting of the thin-walled shell of the electrical connector may be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are provided together with the following description of the embodiments for a better comprehension of the present invention. The drawings and the embodiments are illustrative of the present invention, and are not intended to limit the scope of the present invention. It is understood that a person of ordinary skill in the art may modify the drawings to generate drawings of other embodiments that would still fall within the scope of the present invention.

FIG. 1 show a sectional view of a thin-walled shell of an electrical connector as viewed from a first direction;

FIG. 2 shows a sectional view of a thin-walled shell of an electrical connector as viewed from another direction;

FIG. 3 shows runners for a die-casting mold structure for casting a thin-walled shell of an electrical connector according to one embodiment of the present invention;

FIG. 4 shows a schematic of the die-casting mold structure for casting a thin-walled shell of an electrical connector according to one embodiment of the present invention; and

FIG. 5 shows a cross sectional view taken along the A-A line of FIG. 4.

DETAILED DESCRIPTION

The following paragraphs describe several embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the embodiments are used only to illustrate and describe the present invention, and are not to be interpreted as limiting the scope of the present invention. In FIGS. 3 and 4, the reference numerals include: 1—longitudinal runner, 2—transverse runner, 3—end runner, 4—in-gate, 5—mold cavity of the thin-walled shell of an electrical connector, 6—overflow.

The embodiments of the present invention are for a die-casting mold structure for casting a thin-walled shell of an electrical connector. As shown in FIGS. 3 through 5, the die-casting mold structure includes a runner structure, four mold cavities 5 for casting the thin-walled shell of the electrical connector, and a number of overflows 6. The runner structure includes one longitudinal runner 1, two transverse runners 2, four end runners 3, and four in-gates 4. The longitudinal runner 1, the transverse runner 2, the end runner 3, and the in-gate 4 are connected sequentially. The cross-sectional areas of the longitudinal runner 1, the transverse runner 2, the end runner 3, and the in-gate 4 may decrease progressively in the flow direction of the molten metal. The cross section of the longitudinal runner 1 is oval in shape.

Similarly, the cross section of the transverse runner 2 is oval in shape. The ratio of the perimeter to area of the oval cross section of the longitudinal runner 1 or the transverse runner 2 is smaller than the ratio for a runner with a rectangular or square cross section of the same area.

The longitudinal runner 1 and each of transverse runners 2 are connected by a first curved runner; each of the transverse runners 2 and each of its associated end runners 3 are connected by a second curved runner; and each of the end runners 3 and their associated in-gates 4 are connected by a third curved runner. Each of the first, second, and third curved runners is an arc-shaped structure. The first curved runner has a radius of curvature (R1) greater than 0.45*L1 and less than 0.7*L1 (i.e., 0.45*L1<R1<0.7*L1); the second curved runner has a radius of curvature (R2) greater than 0.4*L2 and less than 0.6*L2 (i.e., 0.4*L2<R2<0.6*L2); the third curved runner has a radius of curvature (R3) greater than 0.3*L2 and less than 0.5*L2 (i.e., 0.3*L2<R3<0.5*L2), where L1 is the length of the associated transverse runner 2, and L2 is the length of the associated end runner 3.

In the embodiment, the shape of the cross section of the longitudinal runner 1 is oval. Similarly, the shape of the cross section of each transverse runner 2 is oval. In other embodiments, the shape of the cross section of the longitudinal runner 1 and the transverse runner 2 is circular. The ratio of the perimeter (also called wet perimeter) to the area of the oval or circular cross section of the longitudinal runner 1 or the transverse runner 2 is smaller than the ratio for a runner with a rectangular or square cross section of the same area. As a result, the resistive and the thermal loss due to the viscosity of the molten or liquid metal can be reduced. In other words, the surface resistance and the heat loss of the liquid metal can be reduced, so that the mold cavities for die-casting the thin-walled shells of the electrical connectors will keep the metal at a high-temperature molten state, thereby alleviating the problem of cold shuts. Furthermore, since the oval or circular cross section of the longitudinal and transverse runners 1, 2 presents walls that are smooth and without any sharp angle, when the walls are subjected to the high speed of the molten or liquid metal of the die-casting process, it is harder for gases to become entrapped in the molten metal because the possibility of local vortexes occurring in the molten metal is reduced.

The wet perimeter described above is the length of the boundary through which the molten or liquid metal of the die-casting process flows to make contact with the mold for the mold cavity. The bigger the wet perimeter, the more energy is lost from the movement of the molten metal.

The dimensions of the cross sections of the longitudinal runner 1, the transverse runners 2, and the end runners 3 are less than the dimension along the lengths of the runners. As such, the velocity vector of a liquid metal at a location of a runner is generally in the same direction as the tangent along the length of the runner near the location. In other words, the component of the velocity and acceleration vector of the liquid metal along the tangential direction of the runner is much greater than the component of the velocity and acceleration vector of the liquid metal normal to the runner. Therefore, in the embodiment of the present invention, the radius of curvature of the first curved runner provided by (0.45*L1<R1<0.7*L1), the radius of curvature of the second curved runner provided by (0.4*L2<R2<0.6*L2), and the radius of curvature of the third curved runner provided by (0.3*L2<R3<0.5*L2) may reduce the energy loss due to the abrupt change of the flow direction and the change in the cross-sectional area of the runners.

Furthermore, experiments may be performed using the die-casting mold structure to obtain acceptable molding quality for the thin-walled shell of an electrical connector. Applying the quality control principles of 6Sigma, it is found that a quadratic function may be used to describe the relationship between the total mass (G), which is the sum of the mass of the thin-walled shell of the electrical connector in the mold cavity 5 and the mass of metal from the associated overflow 6, and the area (A) of the associated in-gate 4. The experiment data is shown in Table 1. The quadratic function is: A=0.8948+0.4292*G−0.01040*G*G.

A method applying the above quadratic function may be used to calculate the area (A) of an in-gate design of a die-casting mold structure for the thin-walled shell of the electrical connector. The method includes:

-   -   (1) Determining an alloy that is applicable to the thin-walled         shell for the electrical connector and setting the density(p) of         the alloy to be 6.8 g/cm3;     -   (2) calculating the sum (G) of the mass of the thin-walled shell         for the electrical connector in the mold cavity and the mass of         the metal from the overflow: G=X+Y, where X: Y=2:1, X is the         mass of the thin-walled shell for the electrical connector in         the mold cavity, and Y is the mass of the metal from the         overflow; and     -   (3) calculating the area (A) of the in-gate:         A=0.8948+0.4292*G−0.01040*G².

TABLE 1 Mass of Mass of Mass of thin-walled thin-walled thin-walled connector connector connector shell in the shell in the shell in the mold mold mold cavity + cavity + cavity + mass of mass of mass of metal from In-gate metal from In-gate metal from In-gate overflow area overflow area overflow area (g) (mm²) (g) (mm²) (g) (mm²) G1 A1 G2 A2 G3 A3 4.190 1.200 19.289 5.280 2.314 1.600 4.153 1.200 18.846 5.280 2.305 1.600 4.151 1.200 19.409 5.280 2.320 1.600 4.181 1.200 19.400 5.280 2.318 1.600 4.089 1.200 19.370 5.280 2.324 1.600 4.136 1.200 19.376 5.280 2.304 1.600 4.189 1.200 19.404 5.280 2.320 1.600 4.166 1.200 19.396 5.280 2.296 1.600 4.199 1.200 19.387 5.280 2.301 1.600 4.862 1.200 13.219 5.280 2.299 1.600 4.232 1.200 18.709 5.280 2.310 1.600 4.089 1.200 13.219 5.280 2.296 1.600 4.862 1.200 19.409 5.280 2.324 1.600 G4 A4 G5 A5 G6 A6 1.634 1.600 3.992 3.279 8.443 3.279 1.637 1.600 3.992 3.279 3.978 3.279 1.637 1.600 3.875 3.279 3.966 3.279 1.610 1.600 3.992 3.279 3.981 3.279 1.632 1.600 3.996 3.279 3.971 3.279 1.637 1.600 3.993 3.279 3.966 3.279 1.633 1.600 3.995 3.279 3.930 3.279 1.632 1.600 3.997 3.279 3.971 3.279 1.633 1.600 3.876 3.279 3.965 3.279 1.646 1.600 3.988 3.279 3.976 3.279 1.633 1.600 3.970 3.279 4.414 3.279 1.610 1.600 3.875 3.279 3.930 3.279 1.646 1.600 3.997 3.279 8.443 3.279

Table 1 shows a relationship between the total mass (G), which is the sum of the mass of the thin-walled connector shell in the mold cavity and the mass of the metal from the overflow, and the area (A) of the in-gate. Using the quadratic function, the area of each in-gate 4 may be obtained quickly according to the practical requirement for the total mass of the casting. Therefore, the time required for designing the die-casting mold structure for the thin-walled shell of the electrical connector may be reduced significantly, thereby enhancing the efficiency of the design process. In addition, the quality of the casting of the thin-walled shell of the electrical connector may be ensured.

The descriptions set forth above are provided to illustrate one or more embodiments of the present invention and are not intended to limit the scope of the present invention. Although the invention is described in details with reference to the embodiments, a person skilled in the art may obtain other embodiments of the invention through modification of the disclosed embodiment or replacement of equivalent parts. It is understood that any modification, replacement of equivalent parts and improvement are within the scope of the present invention and do not depart from the spirit and principle of the invention as hereinafter claimed. 

What is claimed is:
 1. A die-casting mold structure for a thin-walled shell of an electrical connector, comprising: a mold cavity; an overflow; and a runner structure that provides a path for a liquid metal to flow into the mold cavity and the overflow; wherein an area of the cross section of the runner structure is progressively smaller in a direction of flow of the liquid metal, and wherein the cross section of a part of the runner structure has a perimeter-to-area ratio smaller than a perimeter-to-area ratio of a rectangular or a square cross section of the same area.
 2. The die-casting mold structure of claim 1, wherein the runner structure comprises a longitudinal runner, a transverse runner, an end runner, and an in-gate, wherein the longitudinal runner, the transverse runner, the end runner, and the in-gate are connected sequentially, and wherein the end runner connects to the mold cavity at the in-gate.
 3. The die-casting mold structure of claim 2, wherein the cross section of the longitudinal runner is oval or circular, and the cross section of the transverse runner is oval or circular.
 4. The die-casting mold structure of claim 2, wherein the longitudinal runner and the transverse runner are connected by a first curved runner, the transverse runner and the end runner are connected by a second curved runner, and the end runner and the in-gate are connected by a third curved runner.
 5. The die-casting mold structure of claim 4, wherein each of the first curved runner, the second curved runner, and the third curved runner is an arc-shaped structure.
 6. The die-casting mold structure of claim 5, wherein the first curved runner has a radius of curvature R1 greater than 0.45*L1 and less than 0.7*L1 (0.45 L1<R1<0.7 L1), the second curved runner has a radius of curvature R2 greater than 0.4*L2 and less than 0.6*L2 (0.4 L2<R2<0.6L2), and the third curved runner has a radius of curvature R3 greater than 0.3*L2 and less than 0.5*L2 (0.3 L2<R3<0.5L2), wherein L1 is the length of the transverse runner, and L2 is the length of the end runner.
 7. The die-casting mold structure of claim 2, wherein the height H of the in-gate is between 0.2 and 0.5 of the area of the in-gate.
 8. The die-casting mold structure of claim 2, wherein the mass of the thin-walled shell in the mold cavity is twice the mass of the metal in the overflow, and wherein a quadratic function describes a relationship between the area A of the in-gate, and the sum G of the mass of the thin-walled shell in the mold cavity and the mass of the metal in the overflow.
 9. The die-casting mold structure of claim 8, wherein the quadratic function is A=0.8948+0.4292*G−0.01040*G², wherein A is in unit of mm², and G is in unit of g.
 10. The thin-walled shell cast from the die-casting mold structure of claim 1, wherein the metal of the thin-walled shell is an alloy that has a density ρ of 6.8 g/cm3.
 11. The thin-walled shell cast from the die-casting mold structure of claim 1, wherein the thin-walled shell is thinner than 1 mm.
 12. A method for die-casting a thin-walled shell of an electrical connector, comprising configuring a runner structure that provides a path for a liquid metal to flow into a mold cavity and an overflow, wherein an area of the cross section of the runner structure is progressively smaller in a direction of flow of the liquid metal, and wherein the cross section of a part of the runner structure has a perimeter-to-area ratio smaller than a perimeter-to-area ratio of a rectangular or a square cross section of the same area.
 13. The method of claim 12, wherein said configuring comprises configuring the runner structure to have a longitudinal runner, a transverse runner, an end runner, and an in-gate, wherein the longitudinal runner, the transverse runner, the end runner, and the in-gate are connected sequentially, and wherein the end runner connects to the mold cavity at the in-gate.
 14. The method of claim 13, wherein said configuring further comprises: configuring the cross section of the longitudinal runner to be oval or circular; and configuring the cross section of the transverse runner to be oval or circular.
 15. The method of claim 13, wherein said configuring further comprises: connecting the longitudinal runner and the transverse runner by a first curved runner; connecting the transverse runner and the end runner by a second curved runner; and connecting the end runner and the in-gate by a third curved runner.
 16. The method of claim 15, wherein said configuring further comprises: configuring the first curved runner to be an arc-shaped structure having a radius of curvature R1 greater than 0.45*L1 and less than 0.7*L1 (0.45 L1<R1<0.7 L1); configuring the second curved runner to be an arc-shaped structure having a radius of curvature R2 greater than 0.4*L2 and less than 0.6*L2 (0.4 L2<R2<0.6 L2); and configuring the third curved runner to be an arc-shaped structure having a radius of curvature R3 greater than 0.3*L2 and less than 0.5*L2 (0.3 L2<R3<0.5 L2), wherein L1 is the length of the transverse runner, and L2 is the length of the end runner.
 17. The method of claim 13, wherein said configuring further comprises configuring the height H of the in-gate to be between 0.2 and 0.5 of the area of the in-gate.
 18. The method of claim 13, further comprising: setting the mass of the thin-walled shell cast in the mold cavity to be twice the mass of the metal in the overflow; calculating the sum G of the mass of the thin-walled shell cast in the mold cavity and the mass of the metal in the overflow; and calculating the area A of the in-gate from the sum G using a quadratic function that describes a relationship between the area A of the in-gate and the sum G.
 19. The method of claim 18, wherein the quadratic function is A=0.8948+0.4292*G−0.01040*G², wherein A is in unit of mm², and G is in unit of g.
 20. The method of claim 12, wherein the metal for die-casting the thin-walled shell is an alloy that has a density β of 6.8 g/cm3. 